This invention relates to a new low-energy integral thermite igniter/heat source, e.g., for use in igniting larger charges, e.g., propellant charges. The device of this invention is highly efficient especially in terms of energy output versus the amount of material utilized and also has advantageously low gas output.
Various types of igniters are well known. In all prior art devices, there is a non-combustible portion of the igniter which is used to contain the combustible portion. As a result, the energy output of the device as a function of weight and cost of materials is inherently limited. Moreover, most prior art igniters cause evolution of gas which can be very disadvantageous in many uses.
Several such prior art devices are disclosed in U.S. Pat. Nos. 2,777,389; 2,912,931; 3,392,673; 3,434,426; 3,570,405; and 2,743,580. All of these patents disclose igniters having one or several significant disadvantages.
For example, in U.S. Pat. No. 2,777,389, an inert structural material contains a high explosive. The inert structural material inherently dilutes the available energy and reduces the space and the weight efficiency of the device. Of course, this device is explosive, in contrast to the device of our invention. Moreover, the device of this patent incorporates organic polymers which inherently require that a gas will be generated during the explosion.
U.S. Pat. No. 2,912,931 discloses a device which has a combustible container. However, a significant portion of the mechanism is mechanical and non-combustible. The device is used to generate a gas for starting oil wells; thus, it is designed to produce significant amounts of gas and utilizes high gas-yield organic materials and large device sizes.
U.S. Pat. No. 3,392,673 discloses an igniter which is completely consumed. However, the ignition of the containing tube occurs after the igniter has performed its function. Thereby, the weight of the overall device is reduced after ignition. The combustion of the igniter tube does not contribute to the output of the igniter; hence, space, weight and energy efficiency is not enhanced. In addition, many of the operating components are organic, gas-producing materials some of which are not consumable. Again, the device is of a relatively large size.
U.S. Pat. No. 3,434,426 eliminates the need for a separate hot wire igniter by bonding igniter composition directly to propellant surface. Thus, it is necessary to modify the fuse system. The containment deflagration of this invention is not involved.
Accordingly, there continues to be a need for enhancing space, weight, energy etc. efficiency of thermite igniter/heat source devices as well as to minimize the amount of gas which is output upon ignition.